By means of computer simulation, the influence of absorption index, κ, on the accuracy of determining the refractive index, n, of optical materials by the minimum deviation method (prism method) is studied at different measuring angular accuracies from 5'' to 0.1''. The n values within 1.0-4.0 and κ values within 0-0.1 are considered. It is shown that (1) except for the far-infrared region, the error in determining n by formula (1) commonly used in the minimum deviation method, i.e., neglecting absorption, is less than the error due to the accuracy of measuring the prism and minimum deviation angles; (2) the difference between n values calculated with and without absorption taken into consideration is, in most cases, negligible throughout the optical range; (3) however, the total error in determination of n is higher when absorption is taken into account than that in the case when absorption is neglected. The further the increase in accuracy of measuring the angles and sensitivity of radiation detectors, the more the proposed calculation technique will allow one to optimize the prism angle value and to calculate more correctly the values of n and error in its determination.